Prestressed flexible bladed fan

ABSTRACT

A fan having a hub, a plurality of arms extending radially outwardly of the hub, blades, one secured to each arm, which decamber as rotational speed increases, and biasing members, one connected to each arm contacting the associated blade and urging such blade member toward its decambered position and thereby prestressing said blade member.

United States Patent Strick [54] PRESTRESSED FLEXIBLE BLADED FAN [72]Inventor: Karl II. Strick, Chatham, Ontario, Canada [73] Assignee: FranCorporation, E. Providence, R;l.

[22] Filed: April 26, 1971 [21] Appl.No.: 137,123

[52] US. Cl ..416/132, 416/240 [51] Int. Cl ..F04d 29/38 [58] Field ofSearch ..416/132, 240

[56] References Cited UNITED STATES PATENTS 991,331 5/1911 Lawrence..416/132 2,132,133 10/1938 Smith ..416/132 2,374,342 4/1945 Gaubatz.416/132 3,044,557 7/1962 Posh ..416/132 3,289,924 12/1966 Weir ..416/240X [4 1 July 25, 1972 Primary Examiner-Everette A. Powell, Jr.Attorney-W. R. Hulbert [57] ABSTRACT A fan having a hub, a plurality ofarms extending radially outwardly of the hub, blades, one secured toeach arm, which decamber as rotational speed increases, and biasingmembers, one connected to each arm contacting the associated blade andurging such blade member toward its decambered position and therebyprestressing said blade member.

8 Claims, 4 Drawing Figures PRESTRESSED FLEXIBLE BLADED FAN Thisinvention relates to fans having flexible blades which decamber asrotational speed increases.

A principal object of this invention is to increase the pumping, andhence the cooling capacities of flexible bladed fans without increasingthe projected width of the fans and without increasing the number ofblades thereof, or alternatively to reduce the projected width offlexible bladed fans while maintaining cooling capacity at apredetermined level without increasing the number of fan blades. Anotherprincipal object is to substantially reduce fan vibration an concomitantdynamic stresses.

The invention features in a fan having a hub and plurality of fan bladeassemblies comprising arms extending radially outwardly of the hub, andblade members secured to the arms, which decamber as rotational speedincreases, the improvement wherein biasing members are also connected tothe arms and contact the blade members urging them toward theirdecambered positions. In a preferred embodiment, the biasing members aremounted on the downstream sides of the blades and have a continuous baseportion extending radially along the arm and the blade, and a continuousblade contacting outer web portion extending radially along the blade ata position spaced from said arm behind the trailing edge thereof andbehind the trailing edge of a reinforcement member positioned on theupstream side of the blade. The base and outer web portions areconnected by integral triangular shaped fingers having their apicesconnected to the blade contacting web portions and their bases connectedto the other web portions. The biasing member has a configuration whichpermits it to contact the blade throughout its full decambering range.

Other objects, features and advantages will be apparent to one skilledin the art from the following description of a preferred embodiment ofthe invention, taken together with the accompanying drawings thereof, inwhich:

FIG. 1 is a plan view of the upstream side of an engine cooling fanembodying the present invention;

FIG. 2 is an enlarged elevation viewed along the line 22 of FIG. 1;

FIG. 3 is a plan view of the stamping from which the biasing member isformed; and

FIG. 4 is an enlarged end view of an arm and blade assembly taken alongthe line 4-4 of FIG. 2.

There is shown in FIG. 1, generally at 11, an engine cooling fan adaptedfor use in a motor vehicle. The fan has a central planar hub 12, withasymmetrically disposed arms 13 extending radially therefrom. As bestshown in FIGS. 2 and 4, each arm has a twisted section 14 joining it tothe hub so that the plane of each arm is at an acute angle e of to theplane 12a of the hub 12.

A blade structure is secured to the upstream side of each arm 13, andcomprises air-moving or airfoil surfaces formed, as illustrated, on twoseparate portions, a leading member 16 and a trailing blade member 18,respectively designated with reference to the direction of fan rotationshown by the arrow in FIG. 1. The leading member 16 is here constructedas an integral portion of a reinforcement member or cap 24 formed of arelatively rigid steel (SAE 950A, 0.048 inch thick), and defines anextended airmoving or airfoil portion surface, terminating in theleading blade edge 17, the purpose and function of which is more fullydescribed in copending United States patent application Ser. No. 86,750,filed Nov. 4, I970, entitled Flexible Bladed Fan With Extended BladeStructure. The curved trailing blade member 18 is formed of a resilient,more flexible steel (AISI 301 stainless steel, 0.015 inch thick), anddefines an air-moving or airfoil portion surface, terminating in thetrailing blade edge 19, which is substantially parallel to leading edge17. The trailing blade member 18, extending rearwardly from arm 13 agreater distance than the forward extension of leading member 16, formsthe major portion of the blade structure.

A biasing member 34 of resilient, flexible steel (AlSl l stainlesssteel, 0.0l5 inch thick) is secured to each arm 13, at the relativelyrigid leading portion of the blade structure between the arm and theassociated blade member 18 on the downstream side of the blade member.As best shown in FIGS. 2 and 4, the biasing member extends from the arm13 to contact the blade member 18 toward the flexible trailing edge 19behind the trailing edge of the arm 13 to which blade member 18 isconnected.

As most clearly illustrated in FIGS. 2 and 4, biasing member 34 extendsradially along the length of blade member 18 contacting the blade memberadjacent the ends defined by the radial extent thereof and intermediatesaid ends behind the trailing edges of arm 13 and reinforcement cap 24.In the preferred embodiment, as shown in FIG. 3, the biasing member 34if formed from a blank having a base web 35 continuously extending alongthe length thereof. The base web 35 is suitably pierced to receiverivets 25, 29 for assembly on an arm 13. The blank is also die cut toprovide a plurality of triangular shaped fingers 36 having their basesintegrally connected with base web 35. The fingers 36 are in the shapeof isoceles triangles and have a base to altitude ratio of about 1:1.5to approach the characteristic in use of a spring constant which isessentially flat. A blade contacting outer web 37 is integrallyconnected by the apices of fingers 36 parallel to base web 35.

The blank is preformed, after cutting, to a shape approximately asillustrated in broken lines in FIG. 4 in which a flat is provided atbase web 35 and the base of fingers 36. The outer portion of the fingers36 is bent about ashorter radius than that of blade member 18 when it isfully decambered, and the outer web 37 at the apices of fingers 36 isreversely bent about a short radius to provide a height from the flatbase web 35 to the outer web 37 which in an unbiased condition of member34, extends beyond the fully decambered position of blade member 18, asshown in broken lines at 37b in FIG. 4. The curvature of fingers 36 andthe reverse curvature of outer web 37, after assembly, provide atangential contact with the blade member 18 by outer web 37 continuouslybetween the radially defined ends of blade member 18 and a gap from thetrailing edge of arm 13 to the point of contact at outer web 37 betweenthe blade member 18 and biasing member 34.

As shown in FIG. 4, each blade member 18 is sandwiched between areinforcement cap 24 and the arm 13 to which it is mounted on theupstream side of the arm, and is secured to the arm together with thereinforcement cap 24 by rivets 25. Flat 35 of biasing member 34 issandwiched between a corresponding flat portion 28 of blade member 18and arm 13 and is likewise secured to the arm 13 by the rivets 25 whichextend therethrough. The reinforcement cap 24, with integral leadingmember 16, and biasing member 34 are substantially radially coextensivewith the blade member 18, extending radially beyond the end of arm 13,and are secured to the blade member 18, adjacent the outer end thereofby rivet 29 to prevent any tip flutter. The curvature of the fingers 36permits biasing member 34 to extend toward the upstream side of said fanto contact and prestress blade member 18 behind arm 13 at itspredetermined most decambered position at maximum fan rotationalvelocity, as illustrated at 37a in broken lines in FIG. 4, an throughoutthe full range of motion of blade member 18.

The blade member 18 is curved about a radius through the plane of arm 13toward the downstream side of the fan, convexly as viewed in FIG. 1,away from the plane of hub 12,

whereas the leading member 16 is bent toward the plane of hub 12. Theangle a of the chord plane c (FIG. 2) between the leading edge 17 andthe trailing edge 19 with the rotational plane of the fan (which, in theillustrated embodiment, is also the plane 12a of hub 12) is about 38 ina preferred embodiment when, as in the illustrated embodiment, the fanis idle. To provide this chord angle, the airfoil surface 16a iseffectively disposed at an angle d to the arm 13, which is within theacute angle e of the arm 13 to the plane 12 (FIG. 4) of hub 12. Asillustrated, the angle d is about l0.

Reinforcement cap 24 is bent about a radius away from the plane of arm13 at its trailing edge (FIG. 4) and has reinforcing lips 30 and 32which are integrally formed by turning up the edges of cap 24 (aboutone-eighth inch) extending along its inner and outer edges,respectively, to render the reinforcement cap both strong and lightweight. As shown in FIGS. 2 and 4, reinforcement cap 24 extends alimited distance toward the trailing edge 19 of blade member 18, inspaced relationship thereto due to the oppositely directed curvaturesthereof. Preferably, the the biasing member 34 contacts blade member 18behind the trailing edge of reinforcement cap 24.

The arms 13 are arranged for balance of the fan, and the arcuatedistances between the reference lines 40, 41, 42, 43, 44 (drawn radiallyof hub 12 and parallel to the edges l7, 19) are as follows:

Provided at the trailing edge of each trailing blade member 18 is aweight 20. As illustrated, the weight is an integral portion of blademember l8 folded upon itself at the trailing edge so as to engage theconvex side of the blade member and has a mass of about 15 percent ofthe remainder of the blade member 18. Such weights are fully describedin copending United States patent application Ser. No. 857,849, filedSept. 15, 1969, now US. Pat. No. 3,594,098, entitled Fan With WeightedFlexible Blades.

in assembly, the blade member 18, reinforcement cap 24, and biasingmember 34 are first secured together at the outer end by rivet 29 andthen to arm 13 by rivets 25.

In operation, as the fan rotates clockwise, in the direction indicatedby the arrow in FIG. 1, air is moved from upstream to downstream asindicated by the arrows in FIG. 2, by the airfoil surfaces of members 16and 18. As fan speed increases, air pressure and centrifugal forcecauses only the trailing blade members 18 to decamber-in general, tomove toward the plane of hub 12.

Biasing member 34, contacting blade member 18 at outer web 37, followsthe blade member as it decambers. Because the blade member 18 isprestressed by the biasing member 34, the blade member does not deflectas rapidly as an unstressed blade in a comparable fan and the fanaccording to the invention has a greater pumping capacity for a givenprojected width than a fan which does not employ the biasing member. Inaddition, the biasing member dampens vibration virtually eliminatingtorsional vibration modes and severely limiting other modes with aconcomitant reduction of dynamic stress levels.

Other embodiments will occur to those skilled in the art from theforegoing non-limiting description of a preferred embodiment thereof.

What is claimed is:

1. In a fan having a hub and a plurality of fan blade assemblies eachcomprising an arm extending radially outwardly from said hub and aflexible, resilient blade connected to said arm which blade decambersfrom a downstream position, relative to the direction of airflow, to arelatively more upstream position as rotational speed increases, thatimprovement comprising:

a resilient biasing member provided in each of said fan blade assembliesconnected thereto and contacting said blade thereof urging said bladetoward its decambered upstream position and thereby prestressing saidblade.

2. The fan claimed in claim 1 in which said biasing member has a curvedconfiguration with the portion of said biasing member contacting saidblade extending toward the upstream side of said fan, contacting andprestressing said blade at the most decambered position thereof duringrotation of said fan at a predetermined maximum speed, whereby saidbiasing member contacts and prestresses said blade throughout its rangeof motion.

3. The fan claimed in claim 1 in which said blade defines, in

the direction of fan rotation, a generally radially extending leadingportion which is relatively rigid and a trailing portion which isflexible, said biasing member being connected to said assembly adjacentsaid leading portion and contacting said blade on the downstream sidethereof at said trailing portion.

4. The fan claimed in claim 3 in which said biasing member contacts saidblade at said trailing portion continuously throughout the radial extentthereof along a line generally parallel to a generally radiallyextending leading edge defined by said leading portion.

5. The fan claimed in claim 3 in which said fan blade assembly includesa reinforcement member adjacent said leading portion on the upstreamside of said blade, said reinforcement member extending and terminatingtoward said trailing portion in spaced relationship thereto, and saidbiasing member contacting said blade between a trailing edge of saidblade defined by said trailing portion and the point at which saidreinforcement member terminates.

6. The fan claimed in claim 3 in which said biasing member comprises abase portion extending radially continuously along said leading portionand a plurality of integral triangular biasing fingers extendingtherefrom toward their apices at said trailing portion said biasingmember bearing upon said trailing portion adjacent said apices along aline generally parallel to a generally radially extending leading edgedefined by said leading portion.

7. The fan claimed in claim 6 in which said apices are interconnected bya continuous integral outer web of said biasing member said outer webcontacting said trailing portion continuously along said line.

8. The fan claimed in claim 7 in which said biasing member has a curvedconfiguration with said outer web extending toward the upstream side ofsaid fan, contacting and prestressing said blade at the most decamberedposition thereof during rotation of said fan at a predetermined maximumspeed, whereby said biasing member contacts and prestresses said bladethroughout its range of motion.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent ,nna d Julv25.1972

Inventork) i It is certifidtflaf e'rxj'c nr pfgar in theabove-identifiedpatent and thatlsaid Letters Patent are hereby: (iorrected as shown.below:

Change the A's sig riee frbm Fran Corfioratiori" 0 --Fram Corporationp YCol. 1, lin 11-, chan ge qar x" to -and--; Col. 2, lin e. 58;c-harigffan" to and--.

Signeda md sealed this 2nd day of January 1973.

(SEAL) Attest:

EDWARDDM.,PLETCHER,JIR. v ROBERT' GO'TTSCHALK Attestlng Offlcer v vCommissioner of Patents FORM v USCOMM-vDC 60376-P69 U,5. GOVERNMENTPRINTNG OFFICE, [959 0-355'334

1. In a fan having a hub and a plurality of fan blade assemblies eachcomprising an arm extending radially outwardly from said hub and aflexible, resilient blade connected to said arm which blade decambersfrom a downstream position, relative to the direction of airflow, to arelatively more upstream position as rotational speed increases, thatimprovement comprising: a resilient biasing member provided in each ofsaid fan blade assemblies connected thereto and contacting said bladethereof urging said blade toward its decambered upstream position andthereby prestressing said blade.
 2. The fan claimed in claim 1 in whichsaid biasing member has a curved configuration with the portion of saidbiasing member contacting said blade extending toward the upstream sideof said fan, contacting and prestressing said blade at the mostdecambered position thereof during rotation of said fan at apredetermined maximum speed, whereby said biasing member contacts andprestresses said blade throughout its range of motion.
 3. The fanclaimed in claim 1 in which said blade defines, in the direction of fanrotation, a generally radially extending leading portion which isrelatively rigid and a trailing portion which is flexible, said biasingmember being connected to said assembly adjacent said leading portionand contacting said blade on the downstream side thereof at saidtrailing portion.
 4. The fan claimed in claim 3 in which said biasingmember contacts said blade at said trailing portion continuouslythroughout the radial extent thereof along a line generally parallel toa generally radially extending leading edge defined by said leadingportion.
 5. The fan claimed in claim 3 in which said fan blade assemblyincludes a reinforcement member adjacent said leading portion on theupstream side of said blade, said reinforcement member extending andterminating toward said trailing portion in spaced relationship thereto,and said biasing member contacting said blade between a trailing edge ofsaid blade defined by said trailing portion and the point at which saidreinforcement member terminates.
 6. The fan claimed in claim 3 in whichsaid biasing member comprises a base portion extending radiallycontinuously along said leading portion and a plurality of integraltriangular biasing fingers extending therefrom toward their apices atsaid trailing portion said biasing member bearing upon said trailingportion adjacent said apices along a line generally parallel to agenerally radially extending leading edge defined by said leadingportion.
 7. The fan claimed in claim 6 in which said apices areinterconnected by a continuous integral outer web of said biasing membersaid outer web contacting said trailing portion continuously along saidline.
 8. The fan claimed in claim 7 in which said biasing member has acurved configuration with said outer web extending toward the upstreamside of said fan, contacting and prestressing said blade at the mostdecambered position thereof during rotation of said fan at apredetermined maximum speed, whereby said biasing member contacts andprestresses said blade throughout its range of motion.